<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title>Document</title>
	<style>
	div:nth-of-type(1){
		width: 200px;
		height: 100px;
		background-color:green;
		float: left;
		position: relative;
	}
	div:nth-of-type(1)::before{
		content: '';
		width: 20px;
		height: 20px;
		border-radius: 10px;
		background-color: #fff;
		
		position: absolute;
		right: -10px;
		top: -10px;
	}
	div:nth-of-type(1)::after{
		content: '';
		width: 20px;
		height: 20px;
		border-radius: 10px;
		background-color: #fff;
		
		position: absolute;
		bottom: -10px;
		right: -10px;
	}

	div:nth-of-type(2){
		width: 100px;
		height: 100px;
		background-color:red;
		float: left;
	}
	</style>
</head>
<body>
	<p>
	伪元素: 
	缺点: 不生成DOM节点 , 所以无法JavaScript控制
	</p>
	<div></div>
	<div></div>
</body>
</html>